Boron phosphide under pressure: in situ study by Raman scattering and X-ray diffraction

Cubic boron phosphide BP has been studied in situ by X-ray diffraction and Raman scattering up to 55 GPa at 300 K in a diamond anvil cell. The bulk modulus of B0 = 174(2) GPa has been established, which is in excellent agreement with our ab initio calculations. The data on Raman shift as a function of pressure, combined with equation-of-state data, allowed us to estimate the Gr\"uneisen parameters of the TO and LO modes of zinc-blende structure, {\gamma}GTO = 1.16 and {\gamma}GLO = 1.04, just like in the case of other AIIIBV diamond-like phases, for which {\gamma}GTO > {\gamma}GLO = 1. We also established that the pressure dependence of the effective electro-optical constant {\alpha} is responsible for a strong change in relative intensities of the TO and LO modes from ITO/ILO ~0.25 at 0.1 MPa to ITO/ILO ~2.5 at 45 GPa, for which we also find excellent agreement between experiment and theory.